1. Field of the Invention
The present invention relates to a casing of an image sensor. It also relates to a method of making such a casing.
2. Description of the Related Art
A conventional contact-type image sensor may include a casing for holding necessary components such as a light source, light receiving elements, a lens array, etc. To accommodate these parts, the casing is formed with suitably configured inner spaces. Such a casing is made of a resin material by injection molding for example.
The conventional image sensor also includes a transparent cover fixed to the casing. An image-carrying document is brought into sliding contact with the cover to be illuminated by the light source. The light beams emitted from the light source are conducted to the image reading line on the transparent cover through a light conducting passage formed in the casing. The light reflected on the document will pass through the lens array and arrive at the light receiving elements. In accordance with the amount of received light, the light receiving elements output detection signals. For causing the reflected light to reach the light receiving elements, the casing is provided with a second light passage arranged between the image reading line on the cover and the light receiving elements.
The conventional image sensor has been found disadvantageous in the following point.
As stated above, the casing of the conventional image sensor may be formed by injection molding with the use of a resin material. In this instance, however, the resulting casing is liable to be electrostatically charged when the hardened resin material is detached from the mold. Disadvantageously, such static electricity may attract unwanted airborne particles or dust toward the casing. These particles may further be drawn into the light conducting spaces of the casing, where the lingering particles may disturb the passage of light. Further, the particles trapped in the light passages may eventually settle on the inner surfaces of the casing defining the light passages. As readily seen, the presence of these particles is undesirable for the inner surfaces to properly reflect light striking upon these surfaces.
Conventionally, the above problem may be addressed in two ways, as described below.
Specifically, a first way is to use an air blower which is capable of generating a fast-moving air flow toward the casing so that the accumulated dust will be blown away. However, such an air-blowing method may often prove ineffective since the electrostatically adhered dust may often fail to be detached from the casing due to the strong electrical bonding force working between the dust and the casing. Further, even if the dust has been properly detached from the casing, the swirled-up dust (together with other stirred-up particles originally present around the casing) may unfavorably be drawn back to the charged casing and settle on it.
The other or second way to address the conventional problem is to give vibrations or jolts to the casing so that the unwanted dust will be shaken off. However, in this case again, it is difficult to properly detach the dust from the casing due to the strong electrical force.
The present invention has been proposed under the above-described circumstances, and its object is to provide a casing of an image sensor which does not suffer the electrostatic adhesion of unwanted particles.
According to a first aspect of the present invention, there is provided a method of making a casing of an image sensor. The method includes the steps of preparing a casing; and applying a static electricity preventive to the casing.
In accordance with the above method, a light passage may be formed in the casing, and the preventive may preferably be applied to the light passage.
The preventive may be sprayed to the casing. It is also possible to perform the application of the preventive with the use of a movable member to be rubbed against the casing. Preferably, the movable member may be provided with a contact portion brought into contact with the casing. The contact portion maybe solid (i.e., not in the form of a liquid or gas) but elastic, so that the casing rubbed by the contact portion will not be damaged. Preferably, the contact portion may be made of polyurethane rubber.
In the above case, the preventive may be soaked into the contact portion in advance of the rubbing of the movable member.
According to a preferred embodiment of the present invention, the method may further include the step of causing the movable member to remove an unwanted projection formed on the casing. The projection may be a flash formed when the casing is produced by molding from a resin material.
According to a second aspect of the present invention, there is provided a casing of an image sensor. The casing may include a light passage, and a surface defining the light passage. Preferably, this surface may be coated by a static electricity preventive.
According to a third aspect of the present invention, there is provided an image sensor which includes a light source for illuminating an image-carrying document to be read, and a resin casing. This casing supports the light source and is provided with a light passage defined by an inner surface of the casing. Preferably, the inner surface may be coated by a static electricity preventive.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.